1. Field of the Invention
This invention relates generally to fluid pressure regulating valves, and more specifically to two-stage servo gas pressure regulators convertible to separate output pressure ranges, such as those typically used in natural and LP fuel gas controls.
2. Background of the Invention
Fluid pressure regulating valves are widely used in a number of applications. One important application is in the control of gas pressure in gas heating appliances. Typically the heat output such appliances is controlled by metering the combustion gas through an orifice operating on a known and controlled pressure drop. Because the supply conditions for the gas may vary, a pressure regulating valve is used to achieve the known pressure drop, and therefore a known gas flow to the burner. Usually a spring reference is used for maintaining the constant pressure drop, and a service adjustment is provided for fine tuning the regulated pressure. Also, single-stage valve designs are known which facilitate replacement of the reference spring to permit valve conversion for operation with different gases having different characteristics, for example, natural gas and LP gas.
Two-stage gas regulators are used to switch the pressure regulation, and hence the burner heat output, between a low pressure and a higher pressure regulation point. This is often accomplished by a solenoid energized by the heating system control.
Many types of regulating valves have been provided in the prior art to accomplish these tasks. Some have used multiple regulators in one housing, which can lead to complex and expensive assembly. Others have used complex linkages for internal adjustments. Others have provided high and low adjustments which are interrelated, complicating the adjustment process. However, no known two-stage valve designs readily permit reference spring replacement to provide for simple conversion for operation with different gases.